The present invention relates to a rotation angle measuring device.
As a device for measuring an angle of a rotating body, a measuring device and the like provided with an encoder has been known.
As a basic structure of an encoder, the encoder has a rotating plate where a pattern for angle detection is provided and an angle detecting unit for reading the pattern and for measuring an angle.
In a conventional type encoder, a positional relation between an angle detecting unit and a pattern for angle detection exerts influence on an accuracy of angle measurement. Therefore, in order to obtain a high-grade measurement accuracy, a manufacturing must be executed so that there are no deviation between the center of a pattern for detection and the center of a rotation plate, a runout of the rotation plate and de-centering, etc. This has resulted in high manufacturing cost, and also means that higher cost is required to produce a rotation angle measuring device with high accuracy.